Add explicit heap limiting options to pcre2_match(), with associated features

for listing, configuring, etc.

doc/html/pcre2_pattern_info.html

@@ -51,6 +51,7 @@ request are as follows:
   PCRE2_INFO_FRAMESIZE       Size of backtracking frame 
   PCRE2_INFO_HASBACKSLASHC   Return 1 if pattern contains \C
   PCRE2_INFO_HASCRORLF       Return 1 if explicit CR or LF matches exist in the pattern
+  PCRE2_INFO_HEAPLIMIT       Heap memory limit if set, otherwise PCRE2_ERROR_UNSET
   PCRE2_INFO_JCHANGED        Return 1 if (?J) or (?-J) was used
   PCRE2_INFO_JITSIZE         Size of JIT compiled code, or 0
   PCRE2_INFO_LASTCODETYPE    Type of must-be-present information